1. Field of the Invention
The present invention relates to an optical axis adjusting device which is used in an assembly procedure of an optical lens system, e.g., a photographing lens system of a digital camera.
2. Description of the Related Art
In recent years aspherical lenses have been frequently used as a lens element of a photographing lens system of a digital camera and similar optical devices due to the demand for higher resolution and miniaturization. In such a photographing lens system, it is often the case that eccentricity sensitivity of one or more lens groups or lens elements is very high. Accordingly, if the amount of eccentricity of the optical axis of the one or more lens groups or lens elements is not finely adjusted to a minimal amount, an image having a balanced contrast and which is not inclined cannot be obtained, which makes it impossible to improve the optical performance of the photographing lens system. To achieve a high optical performance in a photographing lens system, the amount of eccentricity of the optical axis is required to be within a range of a few micrometers.
To this end, the applicant of the present invention has developed an optical axis adjusting device for use in an assembly procedure of a photographing lens system. According to this optical axis adjusting device, in the assembly procedure a portion of a plurality of lens elements of the photographing lens system is treated as a fixed lens group, while the remaining portion is treated as an adjusting lens group and held by a movable holding device; the holding device is moved in a direction orthogonal to the optical axis of the fixed lens group to align the optical axis of the adjusting lens group with the optical axis of the fixed lens group. However, if the holding device only holds the adjusting lens group loosely, hysteresis occurs during movement of the adjusting lens group, and the adjusting lens group may not be able to move linearly in a worst possible case.